What caused Mother Earth to send the terrible monsters, Typhon and his mate, Echidna, against Zeus?

She was angry that Zeus trapped her children, Titans, and cast them to Tartarus

Explanation:

Mother Earth, called Gaia in Greek mythology, was the mother of Titans, and later also created Typhon.

After Zeus started the war with Titans, in his tenth year he got information from Gaia that he needs  Hundred-Handers and the Cyclopes on his side. He released them and he and his brothers, Poseidon and Hades, good important resources – thunderbolt, trident, and helmet. With these gifts, they were able to conquer Titans and traped them to Tartarus.

However, Gaia, Mother Earth, was very angry because her children were trapped. Because of it, she created Typhon, the monster with the heads of a dragon, and sent him and Echidna to fight Zeus. They have challenged Zeus but were defeated by his thunderbolt. Typhon was trapped as well and buried under Mount Etna.

the answer is chance

a. is the correct answer